1. Field of the Invention
The invention relates to an optical filter device, and more particularly, to a Fabry-Perot optical filter device, which is composed of a Fabry-Perot element operating on the same principle as Fabry-Perot interferometers and a plurality of reflecting elements.
2. Description of the Related Art
The development in optical communication has been focused in the field of technology during the recent years. In addition, the discovery of optical fiber, the maturation of semiconductor process techniques, and the growth of micro-electronic-mechanical process techniques have spurred the optical communication system development with constant advancement.
The optical communication is based on the traveling of light waves, which is used to transmit information, the so-called optical signals. During the information communication, the information transmission and reception quality is greatly influenced by the characteristics of light waves. Generally, optical communication systems include active and passive optical elements. In the optical fiber route, for instance, active elements included may be light transceiver modules, optoelectronic converters. Passive elements included may be fiber couplers, fiber attenuators, fiber filters, fiber isolators, fiber polarizers, wavelength dividers, fiber connectors, optical switches, fiber collimators, fiber circulators, fiber wavelength multiplexers, fiber gratings, fiber amplifiers, and fiber jumpers and leads.
A light wave is of multi-color light wave. Therefore, physical mechanisms such as various light gratings, prisms, or interferometers, Mach-Zehnder interferometers and Fabry-Perot interferometers for example, are required for optical filtering and beam-splitting whenever a information transmission is completed by employing light characteristics of various color lights, what is the main purpose of optical filters. FIG. 1 is the schematic diagram of a typical optical filter device 1 according to the prior art. Referring to the diagram, the optical filter device 1 includes mainly an optical filter element module 2. When an optical signal with wavelengths xcex1xcx9cxcexn is inputted and passed through the optical filter element module 2, an output optical signal of a particular wavelength xcexi is obtained.
Considering the circumstance where a Fabry-Perot device operating on the same principle as Fabry-Perot interferometers is used as the optical filter element module 2 of the optical filter device 1 in FIG. 1, the wavelength distribution of light waves passed through the Fabry-Perot device tend to have a Gaussian distribution. However, the band pass effect of Gaussian distribution is not satisfactory. Take the commonly used standard specification of 100 GHz wavelength channel in fiber communication for example, the stop band is generally defined at xe2x88x9225 dB and the start band at xe2x88x923 dB. In this case, when the light waves pass the Fabry-Perot device once, the stop band of the light waves passed through the Fabry-Perot device will be quite large. Thus, optical signals from neighboring channels would enter, which results in quite large cross talks between each of the channels. Referring to FIG. 2 and FIG. 3. FIG. 2 is a schematic diagram of an optical filter module consisted of n-unit of Fabry-Perot devices connected in series according to the prior art. FIG. 3 is a Guassian distribution diagram of light waves with a particular wavelength 1550 nm passed through an optical filter device consisted of two Fabry-Perot elements connected in series according to the prior art. As shown in FIG. 2, a prior optical filter method using an optical filter device module 2 formed by a plurality of Fabry-Perot elements 201 connected in series is utilized to decrease the stop band of each optical channel so as to reduce the cross talks between each of the channels. As shown in FIG. 3, the horizontal axis represents the light wave wavelength while the vertical axis represents the light wave energy, and the minus sign represents the energy attenuation of the light waves passed. The stop band of the light waves passed through the first Fabry-Perot device (or single cavity) is 7.1 nm, and the stop band of the light waves passed through the second Fabry-Perot device (or dual cavity) is 1.2 nm. Thus, it is observed that the stop bands is in fact decreased apparently by passing an optical signal through a plurality of Fabry-Perot devices, and thereby the cross talk between each of the optical channels is reduced.
Nevertheless, the Fabry-Perot elements with respect to the aforesaid prior optical filter device utilize the principle with respect to optical interference on the optical space between the two reflect surfaces to, control the central wavelength of the filters. Thus, if the space between various Fabry-Perot devices 201 connected in series as shown in FIG. 2 could not be adjusted to be equivalent according to the same central wavelength (that is, the expected particular wavelength xcexi), the optical signal transmission would be surely affected by the improper space adjustment of the Fabry-Perot elements 201 connected in series. However, It is indeed difficult to simultaneously adjust the space to be same for the fact that the smallest light wavelength unit is nm.
In view of the above, an object of the invention is to provide a Fabry-Perot optical filter device, so that a light wave with particular wavelength xcexi is able to pass through a same Fabry-Perot optical filter element more than once, solving the issue of simultaneous space adjustment difficulty occurred in the aforesaid prior Fabry-Perot optical filter devices.
The other object of the invention is to provide a Fabry-Perot optical filter device, so that a light wave with a particular wavelength xcexi is able to pass through a same Fabry-Perot optical filter device more than once, gradually and effectively decreasing the stop bands of the channels, thereby reducing the cross talks between each of the channels.
The Fabry-Perot optical filter device in accordance with the invention includes a Fabry-Perot element that allows a light to pass through and optically filters the light at least twice; and a plurality of reflecting elements that reflect the light passed through the Fabry-Perot device back to the same Fabry-Perot device during the at least twice filtering. The Fabry-Perot optical device further includes an input terminal used to import the light into the Fabry-Perot optical filter device, and an output terminal used to export the light after the at least twice filtering.
In the present invention, the Fabry-Perot device can be a Fabry-Perot Etalon, a wavelength tunable Fabry-Perot resonator manufactured by micro-electro-mechanical-system (MEMS) technique or other elements operating on the same principle as Fabry-Perot interferometers. The plurality of reflecting elements can be various kinds of reflecting mirrors or reflecting prisms provided at the two relative sides of the Fabry-Perot device, so that the Fabry-Perot element can optically filter the light at least twice. The input terminal and the output terminal can be provided as different terminals or the same terminal.
The Fabry-Perot device of a preferred embodiment in accordance with the invention includes a Fabry-Perot element used to selectively and optically filter an optical signal with a particular wavelength xcexi from an optical signal with wavelengths xcex1xcx9cxcexn at least twice; and a plurality of reflecting prisms that reflect the optical signal with wavelength xcexi back to the Fabry-Perot device. In addition, the Fabry-Perot device of the embodiment further includes an input terminal used to import the optical signal with wavelengths xcex1xcx9cxcexn and at least one output terminal used to export the optical signal with wavelength xcexi after the at least two optical filtering.
In the embodiment, the Fabry-Perot element can be a Fabry-Perot Etalon, a wavelength tunable Fabry-Perot resonator manufactured by micro-electro-mechanical-system (MEMS) technique or other elements operating on the same principle as Fabry-Perot interferometers. The reflecting prisms are positioned at two opposite sides of the Fabry-Perot element and can be replaced by all sorts of reflectors, so that the Fabry-Perot element can optically filter the optical signal at least twice. The input terminal and the output terminal are different terminals; the input terminal is aligned with one end of a first collimator and the output terminal is aligned with one end of a second collimator.
The Fabry-Perot optical filter device of another embodiment in accordance with the invention includes a Fabry-Perot element used to optically filter an optical signals with wavelength xcexi from an optical signal with wavelengths xcex1xcx9cxcexn at least twice; and a reflecting prism used to reflect the optical signal with the particular wavelength xcexi back to the Fabry-Perot element. In addition, the Fabry-Perot device of the invention further includes a common input terminal and output terminal used to import the optical signal with wavelengths xcex1xcx9cxcexn and export the optical signal with the particular wavelength xcexi after the at least two optical filtering, respectively.
In the embodiment, the Fabry-Perot element can be a Fabry-Perot Etalon, a wavelength tunable Fabry-Perot resonator, or other elements operating on the same principle as Fabry-Perot interferometers. The reflecting prisms are positioned at the two opposite sides of the Fabry-Perot element and can be replaced by various kinds of reflecting mirrors, so that the Fabry-Perot element is able to optically filter the optical signal with wavelength xcexi at least twice. The common input terminal and output terminal are provided on the same side and share a same collimator.